Field of the Invention
The present invention relates to an improvement of a differential device which distributively transmits rotational force of an input member to a pair of mutually-independent output shafts, the input member retaining a pinion support portion that supports a pinion, and being rotatable together with the pinion support portion. Particularly, the present invention relates to an improvement of the differential device that includes: a pair of side gears each having an outer peripheral portion which includes an annular toothing portion in mesh with the pinion, and connected to the pair of output shafts, respectively; and a cover portion covering an outside of at least one side gear, and rotating integrally with the input member.
Description of the Related Art
In some of differential devices, in order to enhance lubricity on slide contact portions of pinions and an input member, an inner peripheral surface of the input member has been conventionally provided with shallow and narrow oil grooves formed along a peripheral direction of the input member. Such differential devices have been made publicly known as described in Japanese Patent No. 4803871.
However, an oil groove structure of the conventional differential device cannot efficiently collect and reserve a large amount of lubricant oil around the pinions. For this reason, particularly under severe driving conditions such as high-speed rotation of the pinions, there may be a shortage of the lubricant oil supply to sliding portions of the pinions and meshing portions of the pinions and the side gears.
In this case, if back surfaces of the side gears are entirely covered with cover portions from outside of the side gears and the lubricant oil is confined in tightly-sealed spaces surrounded by the cover portions and the input member, the lubricant oil is always supplied to the pinions and their vicinities, and the lubricity thereof is secured. On the other hand, since a certain amount of lubricant oil is confined in the tightly-sealed spaces and no lightening portions are formed in the cover portions, there may occur undesirable things such as: resultant increase in the overall weight of the differential device; easy degradation of the lubricant oil because the lubricant oil in the tightly-sealed spaces is not sufficiently exchanged or cooled; and the like.